Fluxmeter



FLUXMETER Filed April 1, 1946 2d l29 I 28- 23 4'o OBE 2 I9 DIR. .REv. RANGE FIGA Flc-3.5

MAGNETIC FIELD o GAuss INyENToR WILLARD PENN' ATTORNEY eter.

Patented Mar. 24,1 1953 mesneyassignments, tothe-'United -States yof America as represented bythe Secretary ofthe Application April 1, 1946;'seria1No. 658,595

(orgias-1483i 4 Claims. 1 This invention.y relates to A' secondary ffelectrioal measuring equipment and more particularly toa -measuring device for determining thehun-density pf' amagnetic eld.

'The usual practice for measuring the rilux density B of a magnetic -eld' is by means of an exploring coil attached to aballistic vgalvanom- While this method is satisfactory for laboratory use, it is too slow and cumbersome for portable use. In addition, theballistic galvanometer is` delicate and therefore 'requires vcareful handling and cannot be readily moved about.

lllis.invention provides va novel flux meter using a DArsonval4 probe which is 4highly sensitive and whichis of. rugged construction.

, The general object o f this invention isto providea rugged portable instrumentior determiningmagneticflux'density'B.

. Another objectof ,thisinvention is to.; provide an instrument for .determining .magnetic flux density AB which is direct. reading una. .calibrated scale graduated in gauss. l Y

A further object of this .invention is to provide V,an instrument for rdetermining the Valuev of. mag. ,netic ux density B over thenormalmange A.of

values encountered in .working with permanent magnets.

AA still furtherobjectofthis invention .is .to provide an instrument which will `indicate theldirec- .tionof the `lines of force .of a magneticeld.

.Theseand other. Objectswill be. apparent from 4the following specification when takenrwith-lthe accompanying drawings, in which:

Fig.. l isa perspective sketch of one embodiment of the invention as applied to a three range portable gaussmeter.

.Fig 2is. a. diagrammatic `r.ep.resentation of the electrical circuit of'Fig; l.

Fig. 3 is a top view in partial section 'showing the arrangementof thel DArsonval Vprobe incorporatediin the embodiment of Fig. 1 and Fig.2,

Figui is a sectional view along the linev IV--IV Fig.` 5 is aplan View of an instrument dialshowy.ing a representative calibrationsuitable foruseas the indicator with this invention.

Referring toFigs.l1^and 2, an embodiment of the :invention is shown dni-which the magnetic l flux. density B .toJoe measured'maybe readdirlect- 1y on a calibrated scale, such as shown in Fig. 5, on a direct current milliammeter I I. The current to deect milliammeter I I is secured from a battery I2 and controlled by means of a switch I3 and a rheostat I4. A switch I5 is arranged to parallel the meter I I with a resistance I6 when it is in the Set"4 position' vfor the purposev of protecting the lmeter lagainst `overload during adjustmentof the instrument. In order to maintain the current I1 atv al constant value regardless of the'positionof Vswitch I'5 a compensating'resistance I8 is -arranged to `be 4inparallel with resistance i6 vwhen the switch I5 is in the Read position. T-he ohmic value of resistance I 8 must be equal in value to the ohmic resistance of the meter II. It will be apparent that the ohmic value Vof resistance i6 willdepend on the degree of protection deemed desirable for meter II. If= the ohmic "value of the resistance I6 is `made equal to that of 'resistance I8 and of `meter I I, then said Vmeter I I willfdeflect only one half the amount -with the switch I5 in the Setpo"sition that'it would with the switch I5 i-n the Read` position. *The-current I1 isv connected througha switch l 9 toa pair of binding-posts 20 and 2|. The effect ofswitch I9 is to reverse the polarityrof current i1 as it appears at" binding `posts 2IJ and 2|.

The current I1 divides into two'parts at binding posts'ZIl and 2 I. VOne part of the current,2,2, flows througha range selector switch 23 to one of three resistors '24, 2.5, orv 26. lThe ohmic value of resistance 24 is greater than that Ofresistance 25 which in turn is greater than that of resistance 26.

lPosition #l of range switch 23 selects resistor 24,

position "#2A selects resistor 25," and 'position #3 selects resistor 26. Therefore Vposition #l Adf range 4switch 123wi1l below rangeand position #3 will be (high range. The otherpart of the current, 21, flows'through a iieXible. cord 2,8 Vtoa, pair of binding posts'29 and 3Q attached toa DArsonval iprobeV r3l 4and .thence to a coil 32 mounted pivotally within saidprobe'l. lThe sum of current 21 and of current'ZZ is always equal in value to current I1.

It. can'lbe seen that 'the effect of range switch `23is to select .different values of resistance to current22 'thereby changing the proportion of current 212to'the current I'I. Thereforefit can readily be seen that the cleection of meter` I I which is proportional to current Il will also be proportional tdcurrent 21, .the proportionality Vconstant being `selected by means .of range switch 23. .Coil 32 is iiexibly and yieldably held in apredetermined position .by means .of spiral springs 33., and34 which. also-.serve for .electrical vconnections to` thecoil 32. A,fpointer35. is rigidly aixed 'to the coil 32 so that it moves over a marked scale 36 on probe 3 I. The pointer 35 rests normally at a. 0 mark at one extremity of the scale 36, and a Vernier adjustment of spring 33 is provided in order to compensate for any small variables in aesavoc construction and thus assure that the position can be maintained during the life of the instrument.

In operation, the probe 3l is positioned in a magnetic field 3l so that the lines of force of said ield 3! are normal to face 38 of probe 3i. With switch i5 in the Set position, switch I3 in the On position, switch 23 in position #3,

and switch i9 in the Direct position there will be a deflection of pointer 35. If this deflection is toward the Set marl; of scale 36, the direction of the eld is indicated by an arrow 33 imprinted on the case of probe Y3l. Should the deflection of pointer be away from the Set mark on scale 33, it is reversed by placing switch I9 in the Reverse position, which operation indicates that the field is opposite in direction to the arrow 39. With switch i3 set to secure positive deflection, rheostat lli is adjusted until pointer 35 is opposite the Set mark on scale 36. The magnetic ilux density B may be read directly in gauss on the hig-h scale of meter Il by placing switch l5 in the Read position. If the deflection of meter il is not adequate for a good determination of the ux density, the range switch 23 is shifted to a smaller range and the balancing process repeated.

The position of coil 32 in relation to the magnetic field 3? when the pointer 35 is adjusted to the "Set mark on scale 35 may be seen by reference to Fig. 3 which is a partial sectional view of the probe 3l. The axis about which coil 32 is pivotally mounted is arranged parallel to face 3S of probe 3i and thus perpendicular to the lines of force 3? of the magnetic field since it is stipulated that the probe face 38 is positioned so as to be normal to the magnetic iield 31. Also, the coil 32 is so arranged in relation to pointer 35 that the plane of said coil 32 is perpendicular to face 33 and thus parallel with the lines of force 37 of the magnetic eld at all times whenever the pointer is directed to the Set position. This position of coil 32 is desirable since it results in maximum torque being exerted on coil 32 due to interaction of the current 2l flowing in said coil 32 with the magnetic field 3l. This large torque is desirable since it results in an instrument having high sensitivity. It can readily be understood that no portion of the probe 3i must contain magnetic material, even in a, minute degree, otherwise the accuracy of the instrument will be impaired. To this end a very pure metal, such as magnetically pure surgical silver should be used for the windings and connections to coil 32. All other parts are non-metallic and therefore it is not so dicult to select a suitable material for their construction, Among other non-magnetic materials, magnetically pure plastic is suitable for use in the probe 3i. All elements of the instrument except the probe 3l and battery l2 are housed in a case 43 and connection is through iiexible wire cables attached to suitable binding posts.

There has thus been described and illustrated a flux meter for measuring the strength of a magnetic eld (flux density=B consisting of a coil rotatably mounted in a suitable housing, a current source operatively connected to the coil, means for varying the current applied to the coil, and a current sensitive meter which may be calibrated in magnetic field strength units,

such as gauss, for indicating the flux densitt7 of the magnetic field. As heretofore stated the coil is oriented substantially parallel to the lines of iiux in order to provide greater sensitivity.

What is claimed is:

l. A fluxmeter for measuring magnetic ux density consisting of a probe containing a DArsonval meter movement, a current source, means including a current sensitive meter for supplying current from said source to said movement, and means to vary said current to provide a standard deflection of said movement, said current sensitive meter being calibrated in magnetic field strength units for indicating the fiux density of said magnetic field.

2. A fluxmeter for measuring magnetic flux density consisting of a probe containing a coil of wire rotatably mounted and yieldably biased to a predetermined position, a, current source. means including a current sensitive meter for supplying current from said source to said coil, said meter being calibrated in magnetic field strength units, and means for varying the current supplied to said coil to produce a standard deflection of said coil, whereby the iiux density of the magnetic field at said coil is indicated by said meter.

3. A fiuxmeter for measuring magnetic flux density consisting of a probe in the form of a nonmagnetic housing, a coil of wire rotatably mounted within said housing, a pointerrigidly mounted on said coil, means for resiliently biasing said coil to a predetermined position, a current source, means including a current sensitive meter for vsupplying current from said source to said coil, said meter being calibrated in magnetic eld strength units, and means for varying the current supplied to said coil to produce a standard deflection of said pointer, whereby the flux density of the magnetic field at said probe is indicated by said meter.

4. A iluxmeter for measuring magnetic flux density consisting of a probe containing a DArsonval meter movement, the coil of said movement being oriented substantially parallel to the lines of force of said magnetic iiux whenever measurements are made, a current source, means including a current sensitive meter operatively connected to supply current from said source to said coil, means for varying the current applied to said coil to obtain a predetermined deflection of said coil in said field, said current sensitive meter being calibrated in magnetic units for indicating said iiux density.

WILLARD H. FENN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,666,309 Ray Apr. 17,1923 2,010,813 Dysart Aug. 13, 1935 2,335,117 Harrison Nov. 23, 1943 2,338,991 Arnold Jan. 11, 1944 FOREIGN PATENTS Number Country Date 207,680 Great Britain Dec. 6, 1923 

